Reactions between uranium ions

Numerous studies have been made on the forward reaction of the equilibrium. 

Newton and Baker, using wavelengths of 737 m/i or 648 m/i (U(IV) absorption), have obtained similar overall rate coefficients to those obtained by polaro-graphy . However, they have found U(VI) to retard the disproportionation reaction due to the presence of an additional process 

The dimer U2(X1), U204, was detected by its absorption at 737 m/t. Analysis of spectrophotometric data using the rate law 

The reverse reaction of the disproportionation equilibrium has been investigated by Masters and Schwartz. It provides a pathway for the exchange of U(VI) and U(IV) as has been previously mentioned. 

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The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Originally, we were motivated to find ways to remove soluble uranium from water. Thus, we became interested in uranium coordination to carboxylate functions. This led to studies of uranium polymers. The hydrated uranyl ion, U022 + is found in contaminated waters. It is exceptionally stable. Water-soluble uranyl esters form by reactions between carboxylate anions and uranyl cations. Our group and many others sought ways to complex uranyl ions to polymers. This led us to the use of bis-carboxylates to form the uranium polymers represented by 105 below.240,241,242 IF polycondensations and aqueous solution polycondensations were used. Another approach involved making carboxylate complexes of uranyl ions with the sodium salt of poly (aery lie acid).243... 

The reaction rate is also sensitive to chloride ion concentration. The overall reaction between neptunium(iii) and uranium(vi)... 

Although there are quite extensive studies concerning the effect of certain fission products on UO2 deposition in fused chlorides [25, 26], the influence of foreign elements contacting an uranyl-containing melt on the speciation of uranium has been but little studied. For example, some interaction of uranyl(VI) ions with metalhc platinum in a NaCl-KCl melt was noted by Smirnov and Skiba [27] but not by Stromatt [19]. The reaction between U02 and metallic molybdenum in this melt was also observed [26] but the mechanism of the process was not investigated. 

Another example is found in the analysis of the mineral zircon. We had previously published [4] a spectrum of a positive ion laser desorption spectrum of a sample of the mineral zircon (zirconium silicate) showing uranium as 238U+, present in the sample at a level of approximately 15 parts-per-million [41]. The spectrum, which showed mixed zirconium oxides and hydroxides as the most intense peaks in the spectrum, was taken with a four second delay between the laser pulse and ion detection, in order to allow neutrals to be pumped out of the cell. These conditions had been found adequate for analysis of organic compounds. However, it was found that the reactivity of zirconium was such that the mixed oxides and hydroxides were produced as ion-molecule reaction products during the long trap period. 

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